According to Chris Haynes of cleveland.com, the Cavs would 'snatch up' Johnson were he bought out and sign him a veteran minimum contract for the rest of the season. Johnson, however, reportedly doesn't want to be bought out and, if true, it seems likely that he'll finish out the season in Brooklyn.
Johnson would be an interesting signing for the Cavs. He's a scorer first and foremost and could offer the Cavs a boost of some kind off the bench. He wouldn't, however, really help the Cavs better matchup with the Warriors or Spurs in a hypothetical Finals series.
The idea of signing Johnson (or another player who gets bought out) makes sense. After trading Joe Harris to the Magic in a salary dump, Cleveland has an open roster spot. Even though the Cavs have a few trade exceptions to use in a deal, the Cavs don't have a lot of cap room. If the right deal isn't found, signing a veteran to minimum contract might make more sense.